1. Field of the Invention
The present invention relates to a directional control system for a marine vessel, and, more particularly, to a directional control system wherein a stroke of the control element, for example, of the steering wheel, or a position of the control element with respect to the total stroke, is transmitted electrically to a steering device, such as a rudder.
2. Description of Related Art
Directional control systems in the prior art are known as steerage systems, and generally comprise a control element, such as a steering wheel, a rudder wheel or a rudder tiller, and a steering mechanism, which may comprise a rudder blade that is rotatable about a vertical shaft. In alternative or in addition to the rudder blade, the steering mechanism may comprise a sterndrive of an outboard motor or in-outboard motor, wherein the sterndrive bears a propeller and is mounted in a rotatable fashion like the rudder blade.
In the prior art, the steering wheel, the rudder wheel, or the rudder tiller are connected to the rudder blade or the sterndrive of an outboard or in-outboard motor with mechanical devices, such as an arrangement of cables transmitting to the motor sterndrive or blade the rotational motion of the steering wheel or of the rudder wheel, or the angular movement of the rudder tiller. Servo-driven systems are also known in the prior art, wherein the mechanical transmission occurs by means of hydraulic or oil-pressure transmission systems. In these systems, a pump is mechanically connected to the control element and is part of a closed hydraulic circuit comprising a double-acting actuating cylinder and, in some instances, a hydraulic motor. The change in pressure between the two branches of the hydraulic circuit, caused by the movement of the control element due to a manual steering or due to a change in direction of the steering wheel, of the rudder wheel, or of the rudder tiller, causes the actuating cylinder to be actuated in one or the other direction, or causes the hydraulic motor to be rotated in one or the other direction, forcing the rudder blade or the sterndrive of the outboard or in-outboard motor to move angularly.
Yet the directional control systems in the prior art present a number of drawbacks.
A first drawback is that the assembly of purely mechanical and hydraulic systems requires the passage of pull and push cables or of hydraulic piping running through the ship vessel or parts thereof. Therefore, special housings must be provided for the cables or the hydraulic piping, and such housings must be easy to access for control and replacement purposes. Moreover, the housings must be large enough to enable the free sliding of cables within their sheaths, or the passage of pressure fluid pipes of the hydraulic system, as well as the assembly and replacement of such cables and pipes.
Another drawback is the complexity of adding additional, secondary steerage stations, because the mechanical and hydraulic integration of cables and pipes connected to the secondary stations with the cables and pipes already in place is extremely difficult or even impossible without substantial changes to the stations already in place.
Still another drawback is the need to adjust only with mechanical or hydraulic means the function that correlates the position of the steering control element with the corresponding position of the dipped steering mechanism, for instance, the function correlating the angular position of the steering wheel with the angular position of a rudder blade or sterndrive of an outboard motor, only with mechanical or hydraulic means, because the steering control element and the dipped steering mechanism are integrated with a mechanical system (cables and tie rods) or a hydraulic system (connections of fluid piping and possible distribution). Such adjustments must be frequently carried out, since both mechanical systems and hydraulic systems are subject to a degradation in their operating conditions, for instance, to an increase in slacks, a decrease in the amount of fluid, or other wear-related effects. In this situation, a system examination must be carried out for in the entire mechanical or hydraulic system, since cables may broken at any point, and fluid pipes may leak or be broken in different points.
Yet another drawback is the inherent lack of flexibility of the functions correlating the position of the control element with the position of the steering mechanism in the prior art, which prevents these functions from being changed or modified, and also make it problematic to execute or integrate diagnostic and emergency systems and functionalities.
A further drawback is the difficulty in integrating the steerage systems in the prior art within an electronic function control system, for instance, for accelerating or reversing control.